I'd say that the more stations which do have gates, the easier it is to forget at those which don't. If you habitually use stations with gates, touching in and out is hardly even done consciously. It's pretty much just an automatic reflex as you go through. Because different stations have gates or touch in points in different locations, the absence of something at, say, the street entrance, doesn't necessarily activate your brain to think 'this station doesn't have gates, must remember to look for the touch-in point' because the gates might be halfway along a walkway or at the top of some stairs or the entrance to a platform. And once you've passed that street entrance, your brain similarly isn't necessarily noting that there are no gates at the bottom of the stairs to the platforms, because that wouldn't be unusual.
It's not unusual for me to get to the platform of a station with no gates and then genuinely have no memory of whether I touched in somewhere or not.